NSFGEO-NERC: Deciphering the Dynamics of Geomagnetic Excursions

地球磁场最显著的变化是极性偏移和反转。这些事件中，全球磁场强度可能会显着减弱，对于理解在液核中产生和维持地磁场的过程以及可能因地表环境磁屏蔽减少而产生的社会影响至关重要。与逆转相比，偏离得到的关注相对较少，尽管发生得更频繁，持续时间也足够长，可能会造成重大的社会破坏。现在，跨越过去10万年的新观测模型正在以以前无法获得的细节阐明电磁场的演化，并结合场生成过程的数值模拟的进展，这为理解这种神秘事件的新方法铺平了道路。地球磁场的几个全球空间和时间表示覆盖0-100 ka或其子部分，并记录了多达5个具有定性相似性和明显差异的地磁漂移。电磁场扰动、持续时间、局部扰动等的形式定义，可以通过允许与数值地球发电机模拟进行比较的古长期变化指数。将时间间隔扩大到0-120 ka，我们将产生第一个高分辨率的模型，量化的不确定性后布莱克偏移在~95 ka和希利纳帕利偏移在~20 ka。与此同时，数值模拟将建立在当前利兹NERC资助的研究基础上，该研究正在定义“类地球”场行为的要求。本建议的重点是利用这两个相互关联的协同作用部分，增进对地磁漂移的性质和起源的了解。我们将（1）使用新的和现有的全球和时间相关的观测模型，在过去120 kyrs的几次漂移，以表征场的行为之前，期间和之后的偏移;（2）分析偏移机制和可预测性的新的地球发电机模拟进行了主导力平衡，反映了预期的行为，在地球的液体外核;（3）制定正式的标准来定义漂移，并将古油气田行为与当前和新兴的类地数值发电机模拟观点相协调。观测地磁场建模和古长期变化分析以及核心动力学的利兹模拟。观测模型将有助于模拟新的类地标准，而这些标准又将用于对可观测到的场变化进行高分辨率预测，而这些场变化可以在较低分辨率的观测数据中找到。我们期望加强对地磁漂移动态的理解，包括其可预测性及其与极性反转的关系。

The most striking variations of Earth's magnetic field are polarity excursions and reversals. These events, in which the global field strength can significantly weaken, are central to understanding the processes that generate and sustain the geomagnetic field in the liquid core and the societal impacts that could arise from reduced magnetic shielding of the surface environment. Excursions have received relatively little attention compared to reversals despite occurring more frequently and lasting long enough to cause potentially significant societal disruption. Now new observational models spanning the past 100 kyr are illuminating the evolution of excursional fields in previously inaccessible detail, and combined with advances in numerical simulation of the field generation process, this paves the way for a new approach to understand such enigmatic events. Several global spatial and temporal representations of Earth's magnetic field cover 0-100 ka or subsections thereof, and document up to 5 geomagnetic excursions with qualitative similarities as well as distinct differences. Formal definition of excursional field perturbations, duration, local asynchroneity, etc., can be made via the Paleosecular Variation Index allowing comparisons with numerical geodynamo simulations. Expanding the time interval to 0-120 ka we will produce the first high-resolution models with quantified uncertainty for the Post-Blake excursion at ~95 ka and the Hilina Pali excursion at ~20 ka. In parallel, numerical simulations will build on current NERC-funded research at Leeds that is defining the requirements for "Earth-like" field behavior. The focus of this proposal is to improve understanding of the nature and origin of geomagnetic excursions using these two synergistic interlinked components. We will(1) Use new and existing global and time-dependent observational models of several excursions during the last 120 kyrs to characterize field behavior before, during, and after excursions;(2) Analyse the excursion mechanism and predictability in new geodynamo simulations conducted with a dominant force balance that reflects expected behavior in Earth's liquid outer core;(3) Develop formal criteria for defining excursions and reconcile paleofield behavior with current and emerging views on Earth-like numerical dynamo simulations.A vital aspect of this proposal is exploiting existing synergy between the Scripps Institution of Oceanography (SIO) observational geomagnetic field modelling and paleosecular variation analysis and Leeds simulations of core dynamics. Observational models will contribute to new Earth-like standards for simulations, which will in turn be used to make high-resolution predictions of observable field variations that can be sought in the lower resolution observational data. We expect to enhance understanding of the dynamics of geomagnetic excursions, including their predictability and relation to polarity reversals.